From the Department of Pulmonary, Critical Care, and Sleep Medicine (Drs Holley, Petteys, and Collen) and Department of Internal Medicine (Dr Mitchell), Walter Reed National Military Medical Center; and Department of Informatics (Mr Holley), US Army Medical Research Institute of Infectious Diseases.
Correspondence to: LTC Aaron B. Holley, MD, Department of Pulmonary, Critical Care, and Sleep Medicine, Walter Reed National Military Medical Center, 8901 Rockville Pike, Bethesda, MD 20889; e-mail: email@example.com
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
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We appreciate the comments from Dr Jackson and colleagues regarding our recent article.1 Although they state that they recorded relevant variables during their chart review, they do not report Revised Trauma Score or location and mechanism of injury in their abstract.2 It is unclear whether they adjusted for these or other potential confounders when they compared VTE rates between groups. Our models started with > 20 relevant variables in univariate analysis, and we had daily recordings of medication administration and VTE events. We need more of their data to compare their study to ours and determine why we found that enoxaparin 30 mg bid was associated with a reduction in VTE, and they did not.
We would agree that it seems contradictory to say that enoxaparin 30 mg bid has an impact on VTE events but missed dosing does not. The outcomes for missed dosing may have been skewed by patients who were ambulatory and did not require prophylaxis. The 60 patients who had prophylaxis omitted for > 50% of hospital days were younger (aged 25.9 years ± 5.9 years), received fewer transfusions of RBCs (0.0 [0.00-55.0]), had shorter hospital stays (9.5 days [1.0-69.0]), and had lower injury severity scores (16.9 ± 10.9) when compared with the overall group. A portion may have had prophylaxis withheld because they were deemed low risk, thus diluting any harmful effect caused by omissions in higher-risk patients.
Some studies have indicated that delays in initiation may be important,3 and we did not adjust for the timing of omission. We did note that the patients with VTE within 7 days missed prophylaxis for 36.2% of hospital days prior to their VTE.1 We also found that of the 46 patients with clots, 18 (39.1%) were diagnosed prior to admission to our hospital (during the evacuation). Although we did not have access to medical records from the air-evacuation period, we feel our data indirectly support starting chemical prophylaxis as soon as possible and avoiding missed doses. As Dr Jackson and colleagues state in their letter, early evacuation and prolonged flight times markedly increase the risk for VTE. It seems reasonable to recommend using prophylaxis in flight when not contraindicated.
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